Photophysical and redox properties of perylene bis- and tris-dicarboximide fluorophores with triplet state formation: transient absorption and singlet oxygen sensitization.

A detailed photophysical characterization of a couple of new perylene imide derivatives, a carboxylic trisimide PIx, and an asymmetrically substituted carboxylic bisimide PIa is presented. PIx and PIa have the lowest singlet excited state just below 2.6 eV. The dyes are remarkably fluorescent (ϕ(f) = 0.37 ± 0.03 for PIa and ϕ(f) = 0.58 ± 0.04 for PIx in toluene), but they also display an efficient intersystem crossing. This leads to typical excited triplet photophysics/photochemistry, with intense triplet state absorption spectra and efficient singlet oxygen ((1)Δ(g)) photosensitization (ϕ(Δ) = 0.68 ± 0.02 for PIa and 0.44 ± 0.02 for PIx in toluene). On the basis of the measured ϕ(Δ), a ϕ(isc) of 0.65 ± 0.02 for PIa and 0.43 ± 0.02 for PIx in toluene is derived. PIx reduces at -0.58 eV vs SCE, almost similarly to the corresponding symmetrically substituted perylene bisimide PI0, but unlike the latter, it has the first oxidation potential above +1.9 V. PIa is more electron rich and displays a more difficult first reduction at -0.95 V with a more facile oxidation at +1.75 V, similar to that of the parent PI0. The absorption spectra of the excited singlet and triplet states and that of electrochemically generated monoanions are reported.